In semiconductor manufacturing, robots are commonly used to move wafers from one location to another. The use of efficient robots is particularly important for manufacturing processes in which the wafers are subjected to many chemical processes. Because the different processes are carried out in separate reaction chambers, the wafers have to be transported from one reaction chamber to another in a multiple chamber system. U.S. Pat. No. 5,292,393 to Maydan et al. discloses an example of an integrated modular multiple chamber vacuum processing system. A robot employs a dual four-bar link mechanism for imparting selected R-theta movement to the blade to load and unload wafers in the system of Maydan et al. Other robots of a four-bar link configuration are found in U.S. Pat. No. 5,280,983 to Maydan et al. and U.S. Pat. No. 5,452,521 to Niewmierzycki.
Another type of robot arm mechanism is known as the frog-leg type mechanism. U.S. Pat. No. 5,655,060 to Lucas discloses a cluster tool robot that employs a frog-leg type dual arm mechanism driven by a drive system to rotate and to stretch or translate in and out of process modules. U.S. Pat. Nos. 5,435,682 and 5,020,475 to Crabb et al., disclose substrate handling subsystems employing frog-leg mechanisms for moving wafers or substrates to and from processing subsystems. A frog-leg robot having walking-beams is disclosed in U.S. Pat. No. 5,569,014 to Hofmeister.
The robot speed is one key factor that limits the production capability or throughput of the equipment, especially in processes that require quick and frequent transport between chambers. To achieve higher throughput, a pair of four-bar link arms have been used to operate a pair of robot blades that are stacked together and spaced from one another. The two robot arms rotate together, but may move in and out independently. After the robot rotates the arms to a chamber and aligns the upper arm with the chamber inlet, the upper arm moves into the chamber to load or unload a wafer. The upper arm is then withdrawn from the chamber, and the robot moves the arms vertically upwardly to align the lower arm with the chamber inlet. The lower robot arm then moves in and out of the chamber to load or unload a wafer. The use of the dual robot arm mechanism essentially increases the overall speed of the robot. While the use of the dual arms increases throughput, the requirement for vertical movement of the robot arms decreases the overall speed and may be undesirable in certain systems.